The oral mucosal surface represents an interface with the external environment, and as such, is a first line of defense against microbial colonization and infection. Lipids at the mucosal surface and in saliva are thought to underlie at least part of an antimicrobial barrier. Some of these lipids are synthesized in the epithelium and are carried to the surface as cells differentiate, while others are secreted onto the surface from sebaceous glands. Published reports and preliminary data indicate that free sphingoid bases have broad antimicrobial activity, and our previous studies demonstrate the presence of these bases at the mucosal surface and in saliva. In addition, our preliminary results demonstrate potent antibacterial activity associated with a specific fatty acid (C16:1_6) derived from sebaceous triglycerides. C16:1_6 has been shown to act synergistically with low concentrations of ethanol and is capable of killing an isolate of Staphylococcus aureus that is resistant to both methicillin and mupirocin. The proposed studies are designed to better develop our understanding and ability to exploit these natural antimicrobials through pursuit of four Specific Aims: 1. To determine the variability in the quantity and composition of lipids in the oral cavity in a human population. 2. To delineate antimicrobial activity of C16:1_6 and free long-chain bases (sphingosine, dihydrosphingosine, phytosphingosine and 6-hydroxysphingosine) against selected strains of the periodontal pathogens Porphyromonas gingivalis and Actinobacillus actinomycetemcomitans. 3. To document the bactericidal effects of C16:1_6, sphingosine, dihydrosphingosine and 6-hydroxysphingosine, in combination with antimicrobial peptides or permeabilizing agents such as ethanol, against the test microorganisms. 4. To identify mechanisms by which the antimicrobial lipids act. Effects of the antimicrobial lipids on overall appearance and biochemistry of test bacteria in culture will be determined, and the interaction of these lipids with model membranes will be studied. The proposed studies could lead to a significant set of tools for combating bacterial infections, including periodontal disease, and could provide new tools to use against increasingly antibiotic-resistant bacteria.This project will test the hypothesis that certain lipids present at the oral mucosal surfaces and in saliva are antimicrobials effective against periodontal pathogens. To test this hypothesis a series of studies will be conducted to document variation in the concentrations of lipid and their activity mechanisms of action against selected bacteria when used alone or in combination with other antimicrobials.